1. Field of the Invention
The present invention relates generally to wireless communications systems, and specifically to a system that is capable of switching subscriber units from cellular wide area network coverage to ad hoc network coverage.
2. Description of Related Art
In conventional wide area network cellular systems, localized, or neighborhood, coverage, including in-building coverage, often cannot be guaranteed, as it would be cost prohibitive and impractical to install base stations for all indoor and outdoor locations within a service area. Consequently, system planners often only guarantee 90-95% coverage within a service area.
In addition, guaranteed neighborhood wireless coverage is impractical because the call model for such coverage is much different than that for traditional cellular coverage. Specifically, calls within such a localized area are typically much longer in duration and are often more frequent among a higher percentage of subscribers. The resulting load associated with providing such coverage would consequently require the installation of a large number of small footprint cells in a conventional cellular system to ensure coverage to a given neighborhood or building complex. Such coverage might be cost prohibitive, as users of the localized service would probably expect usage costs that were equivalent to landline system usage costs.
In order to provide such localized service at usage costs equivalent to landline usage costs, neighborhood service would have to be tiered so that service within the neighborhood would have one associated cost, while transition to service outside the neighborhood would have a different associated cost. However, traditional cellular systems cannot effectively control such transitions. For example, in CDMA type systems, deployment of microcells or picocells effectively punches holes in the wide area coverage so that any user who comes within range of such cells must be serviced by the cells to avoid co-channel interference from these cells. Unfortunately, as a result, the capacity of a cell reserved for servicing the neighborhood would be reduced.
If the deployment of a microcell or picocell utilized a carrier frequency that was different from the adjacent wide area network coverage, then it would be possible to prevent non-subscribers from utilizing the neighborhood resources by denying handoffs to non-subscriber handoff candidates. However, such a solution would still be costly to implement due to the backhaul required for each neighborhood microcell and/or picocell. In addition, the equipment required to implement each neighborhood cell, and the deployment and maintenance of such equipment, would be costly. Also, adjacent neighborhoods would still have to share resources to, for example, facilitate soft handoffs whenever a subscriber was in a boundary region to avoid co-channel interference from carrier frequencies shared by neighboring cells.